The present invention is directed to electrical shift control devices for bicycle transmissions and, more particularly, to a motion sensor for use with a bicycle sprocket assembly.
Motion sensors are commonly used with bicycles to sense rotation of the wheel or pedal crank so that bicycle speed and cadence may be computed by a bicycle computer and displayed to the rider. Such information also may be used to control an automatic or semi-automatic bicycle transmission, wherein the bicycle speed or cadence may be used to determine when to change gear ratios. The typical motion sensor usually comprises a magnet attached to the wheel or crank arm and a magnetic sensor attached to the bicycle frame. When the magnet passes in close proximity to the magnetic sensor, the sensor provides a pulse to the bicycle computer. The speed or cadence then may be computed based on the elapsed time between successive pulses.
A disadvantage of traditional motion sensors is that they increase the number of parts at various locations on the bicycle, thus giving the bicycle a cluttered appearance. Furthermore, the appearance of a magnet rotating with the spokes can be disconcerting. Also, as the number of electronically controlled components increases, the amount of wiring needed to connect the various components together also increases. For example, if the bicycle uses an electronically controlled transmission, then wires must be routed for the wheel magnetic sensor, the crank magnetic sensor, the front transmission and the rear transmission. The aesthetic appearance of the bicycle is greatly diminished by such excessive wiring.